1. Field of the Invention
This invention relates to a non-volatile semiconductor memory device (EEPROM) and an electric device with the same.
2. Description of Related Art
In a conventional NAND-type flash memory, one block serves as a unit of data erasure, and one page as a unit of data read and write. Here, one block is defined as a group of NAND cell units with a shared word line, and one page is defined as a group of memory cells arranged along a word line.
In the NAND flash memory, to over-write data into a block, it is necessary to do write operations by a page after having erased the block. Therefore, in case it is required to rewrite a part of the block data, it is necessary to copy to-be-restored page data into another block (i.e., spare block), which has already been erased. This data copy is performed by repeating a page copy with reading data by a page and writing the read data into another block by a page (for example, refer to Japanese Patent Application Laid Open. No. 2003-233992).
However, repeating the above-described page copy, dada bits of the non-selected cells are disturbed in each read and write operation, thereby being likely to be inverted partially. To deal with the problem, it is required to prepare an ECC circuit for error checking and correcting the read data at each page copy reading time.
In detail, it is assumed that one page of a NAND-type flash memory is constituted by a normal data area of 2 KByte, and a redundant area of 64 Byte where various management data Including ECC data are stored. Data read in the page copy is performed by a page from the cell array to the page buffer, and data output of the read data is performed by serial transferring by a byte from the page buffer to the I/O terminals. Therefore, it is required to repeat the data output operation, error-checking, error-correcting and data write back into the page buffer 2112 times for one page copy operation. If the frequency of error appearance is not high, the error checking and correcting in the page copy will become a waste of time.